1. Field of the Invention
The present invention relates to a color solid-state image capturing apparatus having a photoelectric conversion section (which is defined as a light receiving section corresponding to each pixel) configured with a semiconductor element (photodiode), which performs photoelectric conversions on and capturing incident light from a subject for each pixel, and a plurality of microlenses for focusing incident light through corresponding color filters of respective colors on corresponding light receiving sections; and an electronic information device, such as a digital camera (e.g., digital video camera and digital still camera), an image input camera, a scanner, a facsimile machine, and a camera-equipped cell phone device used in an image capturing section as an image input device.
2. Description of the Related Art
A conventional color solid-state image capturing apparatus includes a plurality of light receiving sections formed on a light receiving surface of an image capturing area, the light receiving sections being arranged with a plurality of photoelectric conversion sections in two dimensions (transverse and longitudinal directions) corresponding to respective pixels. A light signal entering each of the light receiving sections is converted into an electric signal at each light receiving section. A single-plate color solid-state image capturing apparatus is known, in which color filters of respective colors are repetitively arranged with a constant space period on each light receiving section, thereby obtaining a plurality of color signals (e.g., color signals of three primary colors of R, G and B) by one image capturing apparatus. In particular, with the advancement of the miniaturization of the pixel size, a structure formed with a plurality of microlenses for focusing light in a corresponding manner to each light receiving section is widely used in order to increase the efficiency of light entering to each light receiving section.
In such a conventional color solid-state image capturing apparatus, the response for each color in each light receiving section is not constant due to various reasons, causing inequality of the response. As a result, a color shading occurs in the periphery of the light receiving surface in the image capturing area. As a well known example with the use of an interference-type infrared rays cut filter with a dielectric multilayer film, as the position (distance) moves further away from the center section of the light receiving surface of the image capturing area to the outside, an infrared cut wavelength shifts to the short wavelength side and a red color signal decreases, causing the periphery of the light receiving surface of the image capturing area to be blue.
Thus, the fact that the red color signal decreases at the periphery section of the image capturing area to be turned to a blue color, is disclosed in Reference 1 and will be described in detail with reference to FIGS. 5(a) and 5(b).
FIG. 5(a) is a schematic view illustrating a structure of a section of the conventional color image-capturing system disclosed in Reference 1. FIG. 5(b) is a schematic view illustrating a plan structure of a light receiving surface of an image sensor in FIG. 5(a).
In FIG. 5(a), a color image capturing system 100 includes: an image sensor 101 for capturing incident light; a package 102 for accommodating the image sensor 101 within; a lid glass 103 provided on the light entering side of the image sensor 101 inside the package 102; an infrared rays cut filter 104 formed by a dielectric multilayer film provided on the lid glass 103; and an image forming lens 105 for forming an image on a light receiving surface of an image capturing area of the image sensor 101, provided above the infrared rays cut filter 104.
An optical axis C of the image forming lens 105 passes the center section of a light receiving surface (image capturing area) of the image sensor 101, and a light incident angle θ in the optical axis C is 0 degree. The incident angle θ increases from the center section of the light receiving area (image capturing area) to a periphery section (circumference section), and the incident angle becomes a maximum value θ 1 at the outer circumference edge section (corner section). FIG. 5(b) illustrates such increase of the incident angle. In FIG. 5(b), the maximum value θ 1 is the incident angle θ corresponding to a rectangular corner section 101a of a light receiving surface 101A (image capturing area) of the image sensor 101 farthest from the optical axis C at the center section of the light receiving surface 101A (image capturing area) of the image sensor 101. Herein, the position of a concentric circle having the optical axis C as the center of the light receiving surface 101A shows the positions having the same distance from the optical axis C.
On the other hand, it is needless to say that a conventional solid-state image capturing device with a higher resolution is preferable. It is known that the resolution is improved by increasing the brightness signal. As a result, there is a demand for improving the brightness signal.
The brightness signal can be obtained by a predetermined equation with values of respective color signals as variables. The equation for obtaining the brightness signal uses one of the values of respective color signals as a maximum component. Thus, it is effective to increase the color signal having the maximum component that significantly contributes to the brightness signal in order to increase the brightness signal. For example, in accordance with a common standard, or the NTSC standard, a brightness signal Ey is defined by an equation Ey=0.59Eg+0.3Er+0.11Eb. Herein, Eg is a signal component of green (G), Er is a signal component of red (R), and Eb is a signal component of blue (B). As described above, the contribution of the signal component of green (G) is large in the brightness signal. Therefore, it is more effective to increase the signal component of Eg than to increase signals of other colors in the NTSC standard so as to increase the brightness signal.
As described above, the brightness signal uses one of the plurality of color signals as the maximum component. As a conventional technique for increasing a color signal of the maximum component in order to increase the brightness signal, Reference 2 will be described in detail with reference to FIG. 6.
FIG. 6 is a main part cross sectional view of a conventional solid-state image capturing device disclosed in Reference 2. Herein, a transfer gate wiring and a control gate wiring will be omitted in order to avoid the complexity of the description.
In FIG. 6, a conventional solid-state image capturing device 200 is provided with a plurality of embedded type photodiodes 202, which functions as a light receiving section, in two dimensions on an n-type silicon substrate 201. The embedded type photodiode 202 is provided with a predetermined area for receiving light by a vertical signal line and an opening 204 of a control area wiring 203. Although not illustrated in the figure, the embedded type photodiode 202 is composed of an n-type area surface diffusion section provided on a surface of the n-type silicon substrate 201 and a p-type charge accumulation area provided further inside the n-type silicon substrate 201.
Above each of the embedded type photodiodes 202, a color filter 205 of any one of color layers of R, G and B is positioned in an on-chip state above an insulation film 206. Note that the Bayer arrangement is adopted as a color arrangement for the color filter 205. The color filter 205 has the same width W-4 and the same area for each R, G and B. The color filter 205 is positioned in a corresponding manner to the embedded type photodiode 202 for performing photoelectric conversions. As a result, incident light is led to the embedded type photodiodes 202 subsequent to passing through the color filter 205.
Above the color filter 205, a microlens 207 is positioned in a corresponding manner to the color filter 205, in an on-chip state above a planarization film 208. The microlens 207 is positioned in a corresponding manner to the color filter 205. The color filter 205 is positioned in a corresponding manner to the embedded type photodiodes 202 as described above. Thus, the microlens 207 is positioned substantially in a corresponding manner to the embedded type photodiodes 202.
The microlens 207 has a different diameter depending on a color layer of the corresponding color filter 205. Herein, the diameter W-1 of a microlens 205G positioned in a corresponding manner to a color filter 205G of a color layer of G (green) is comparatively larger than a diameter W-2 of other microlenses 205R and 205B. Thus, the pixel for obtaining a G signal has more light focusing ratio than pixels of other colors, thereby increasing the amount of the incident light. Accordingly, the intensity of the output signal of the G signal increases.
Note that the conventional solid-state image capturing device 200 adopts the NTSC standard. In the NTSC standard, the G signal of green color is the maximum component of the brightness signal. Therefore, as described above, the resolution of the conventional solid-state image capturing device 200 increases as the maximum component of the brightness signal increases.
In the conventional solid-state image capturing device 200, a microlens 207G, which corresponds to a color layer 205G of a green color filter functioning as an intense brightness color layer, has a larger opening area than a microlens 207R or 207B which corresponds to other color layers. Herein, the diameter of the microlens 207G corresponding to the intense brightness color layer is increased more than that of conventional microlenses. Therefore, the intensity of the G signal due to the intense brightness color layer increases.
However, the area for elements is limited. As the microlens 207G becomes larger, the microlenses 207R and 207B, which correspond to other color layers, will become smaller accordingly. However, the diameter W-2 of the microlenses 207R and 207B is larger than the opening width W-3 of the control area wiring 203. As a result, pixels corresponding to dim brightness color layers will have an improved light focusing ratio by positioning the microlenses 207R and 207B.
Although the diameter W-2 of the microlenses 207R and 207B becomes smaller, the ratio of the signal of the intense brightness color layers will increase relative to the signal of the dim brightness color layers. As a result, the brightness signal can be increased and the resolution can be improved by calculation and correction outside the solid-state image capturing device.    Reference 1: Japanese Laid-Open Publication No. 2005-234038    Reference 2: Japanese Laid-Open Publication No. 2006-86356